Environmental
Change in the Great Basin: Tracking Cheatgrass Invasion with Remote Sensing

Land use legacies of ecosystem disturbance (eg. grazing, agriculture)
in the Great Basin, US have been shown to enhance the spread of invasive
species, in particular cheatgrass (Bromus tectorum) (Figure 1). Cheatgrass
is a critical problem in the west because its presence changes ecosystem
function, leads to increased fire frequency, and creates unpalatable
rangeland for livestock. We identify the regional extents of cheatgrass
invasion by identifying cheatgrass based on its unique, interannual
amplified response to rainfall using Advanced Very High Resolution Radiometer
(AVHRR) time series (Figure 2). Areas with extensive invasions occur
in northern Nevada, near the Humboldt River, and in central Utah, near
the Bonneville salt flats (Figure 3). We then scale down to a Landsat
time series in the highly invaded area of northern Nevada to understand
the process of cheatgrass invasion over the last 30 years. Landsat data
show that current invasion is primarily driven by fire, which destroys
native shrubs and clears the way for cheatgrass establishment. However,
cheatgrass is also spreading extensively via windblown dispersion. Characteristics
of the ecosystems into which cheatgrass is able to spread most readily
will help us to improve land management techniques to slow invasion.

Figure 2: AVHRR time series of a native ecosystem (black) and a cheatgrass
dominated ecosystem (green) show that cheatgrass has an amplified response
to rainfall.

Figure 3: A regional map of amplified response in the Great Basin shows
the likely distribution of cheatgrass dominated ecosystems. Cheatgrass
dominance is concentrated in northern Nevada and central Utah.